This invention relates generally to a rodent cage which may be used as a static unit or in connection with a ventilated cage and rack system and, in particular, to a rodent cage that may be used for a variety of rodent types including but not limited to rats, mice, gerbils, hamsters and guinea pigs.
Ventilated cage and rack systems are well known in the art. One such ventilated cage and rack system is disclosed in U.S. Pat. No. 4,989,545, assigned to Lab Products, Inc., in which an open rack system including a plurality of shelves, each formed as an air plenum is provided. A ventilation system is connected to the rack system for ventilating each cage in the rack.
In prior art ventilated cage and rack systems, cages of different sizes are used to accommodate rodents of different types. These cage sizes are selected according to Institute Laboratory Animal Resources (ILAR) guidelines which set non-binding minimums for the size and dimension of cages for particular rodents. For example, for mice that weigh more than 25 grams, a cage having a dimension of at least 15 square inches per mouse is required. Similarly, rats up to 400 grams in size require a cage of at least 40 square inches per rat. Similar requirements are mandated for hamsters and guinea pigs by the Animal Welfare Act (AWA).
A drawback of the prior art cages is that a variety of different cage sizes, necessary to support the different rodent types, must be inventoried and managed so that the appropriate cage size is available for a particular study. This problem is exacerbated in large research facilities, for example, the National Institute of Health (NIH), where 20 to 30 different cage sizes have to be coordinated. Furthermore, each different cage size requires that the corresponding rack that supports the particular cage size and corresponding accessories be used. This forces the facility to inventory and manage a variety of different rack sizes as well. Accordingly, it would be desirable to provide a single cage size which is suitable for different rodent types thereby simplifying the maintenance of cage and rack systems.
The prior art cages include a cage bottom having four walls and a base with an open top. A wire bar lid, that stretches across the top of the cage bottom and extends into the cage bottom, is disposed between the cage bottom and bonnet. A bonnet supporting an air filter thereon is placed on top of the cage bottom wire bar lid thereby covering the cage bottom. The wire bar lid is constructed from stainless steel and supports food and water in the cage while also preventing the rodents, particularly rats, from gnawing through the bonnet and damaging the filter or escaping from the cage.
Several problems exist with the use of the wire bar lid in the prior art cage design. First, because the wire bar lid extends into the cage bottom, it creates an artificial ceiling between the cage bottom and the bonnet thereby reducing the amount of area and height available for the rodents. Also the wire bar lid must be removed to provide access to the animal requiring labor and work space for placing the lid during use. Also, the wire bar lid prevents the bonnet from sitting flush on the cage bottom thereby allowing air to either escape or enter the cage bottom over the lid wires creating a Venturi effect in a ventilated cage environment. Although this problem is most pronounced when rounded wire bar lids are used, it nevertheless exists even when flat rimmed wire bar lids are employed. Accordingly, it is desirable to provide a rodent cage in which a wire bar lid is not required so that the usable area for rodents is maximized and ventilation to the cage is improved.